Toshihiro Shimada

Work functions and photothreshold values of various layered metal dichalcogenides ( ZrSe 2 , HfSe 2 , NbSe 2 , 1T-TaS 2 , 2H-TaS 2 , MoS 2 , MoSe 2 , α-MoTe 2 , SnS 2 , SnSe 2 ) have been measured by a photoemission technique. The measured photothreshold values, except for Sn compounds, are compared with the calculated values based on various band models. The agreement between the observed and calculated values is satisfactory for most of the materials.

New sources of selenium and sulfur for UHV preparation of thin films are described. These sources, utilizing the high temperature thermal decomposition of SnSe2 and SnS2, are bakeable to at least 300 °C providing much more convenience than element Se and S sources. The thermal decomposition is studied with thermal gravitometry, mass spectrometry, and x-ray photoemission spectroscopy. The utility of the sources is demonstrated by the epitaxial growth of TiSe2 on MoS2.

Copper phtalocyanine (CuPc) films with the thickness controlled in molecular scales have been grown epitaxially on (0001) surfaces of layered materials, and electronic interaction at the interfaces have been studied by photoelectron spectroscopy. Materials with different electronic properties having different work functions (Evac) were chosen as the substrates; semiconducting MoTe2 (Evac=4.0 eV), semi-metallic highly oriented pyrolytic graphite (Evac=4.5 eV) and metallic TaSe2 (Evac=5.5 eV). For

Hydrogen-terminated vicinal Si(111) surfaces provide quasi-van der Waals substrates with regularly spaced atomic height steps for the epitaxy of organic material films. Molecular beam epitaxy of vanadyl and copper phthalocyanines (VOPc and CuPc) was attempted on just-cut and 7°-miscut surfaces in order to investigate the effect of the steps on the epitaxial growth feature. The molecular arrangement of the films was characterized by a new technique using multiple-azimuth reflection high energy el

The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities.